The study investigates correlates and determinants of fertility differentials in 1900 among the U.S. population. At the time, the American population was in transition from high to low fertility and was characterized by substantial internal variation in reproductive patterns across geographical regions and social groups. The basic data source is a sample of 100,924 individuals which were sampled from the U.S. Census manuscripts. The research will relate major patterns to those identified in studies of other fertility transitions at the time.